How do you know an actor or actress is not performing in a shoot because they were forced to? How do you know the editor hasn't cut out the parts where the model revoked consent between shots? You'll have to review the entire making-off process and confidential interviews with all participants to find out that the people on camera actually consented or were merely forced to do so.

Then there is porn which specifically focuses on vulnerability, humiliation, power balances, trust, you name it.

I don't think most porn is nonconsensual, especially not most professional grade stuff, but I know for sure there is a percentage of "consentual" porn that's actually based on faked or revoked consent because human traffickers can make big money on platforms like Pornhub and Onlyfans. It's the only logical conclusion, you don't need to be a criminal mastermind to think of this.

The legal definition of consent and exploitation is the easy part: there is no consent until it's freely given, and consent can be retracted at any point. Any non-consensual activity is abuse and exploitation. Easy peasy, covers pretty much everything. The verification process is where the actual problem lies. You obviously can't have people sign a document (because people can easily be coerced). Even in full production pornos where the people on screen seemed professionals doing their job, produced by dedicated companies and sold to the public on VHS tapes, turned out to be rape years after the fact, and people who bought those might never find out.

It's a practically unsolvable problem.